The proposed studies have three major goals: (A) Neurological diagnosis of spinal cord injury can be improved by defining the sensory capacities that depend critically upon transmission along the dorsal spinal columns. This major somatosensory pathway has been investigated thoroughly by anatomical and physiological techniques, but psychophysical investigations are needed to determine the functional significance of organizational features that have been described. (B) The mechanical factors that determine the sensitivities of cutaneous receptors can be described by application of video analysis techniques to microscopic views of the skin during indentation. This analysis will focus on the non-hairy (glabrous) skin of primates that is specialized for exquisite tactile sensitivity. (C) In order to improve understanding of the participation of spinal cord circuitries in the control of pain, pharmacological compounds will be introduced directly on the spinal cord (intrathecally), and both sensory and motor capacities will be evaluated thoroughly. By comparing the effectiveness of a variety of opiate agonists in modulating pain reactions without producing other effects, improved methods of pain therapy can be suggested. The proposed studies will be conducted with monkeys, because the spinal pathways are quite similar among primates but differ considerably between primates and other mammals. The stimuli uitilized in these are brief, non-injurious and easily tolerated by monkeys and humans. This is a multidisciplinary approach within the Neurosciences, involving direct correlations of anatomical and physiological data with highly quantitative evaluations of sensory thresholds and motor reactions to precisely controlled somatosensory stimuli.